High-Latitude Geomagnetic Secular Variation at the End of the Cretaceous Normal Superchron Recorded by Volcanic Flows From the Okhotsk-Chukotka Volcanic Belt

The Cretaceous Normal Superchron (CNS, 84-121 Ma) is a singular period of the geodynamo's history, identified by a prolonged absence of polarity reversals. To better characterize the paleosecular variation (PSV) of the geomagnetic field at the end of this interval, we sampled seven continuous sequences of lava flows from the Okhotsk-Chukotka Volcanic Belt, emplaced 84-89 Ma in the vicinity of the Kupol ore deposit (NE Russia). From a collection of 1,024 paleomagnetic cores out of 82 investigated lava flows, we successfully determined the paleodirections of 78 lava flows, which led to 57 directional groups after removing the serial correlations. The resulting paleomagnetic pole is located at 170.0 degrees E, 76.8 degrees N (A95 = 5.2 degrees, N = 57), in good agreement with previous estimates for north-eastern Eurasia. Aiming at quantifying PSV at a reconstructed paleolatitude (lambda) of similar to 80 degrees N, we obtained a virtual geomagnetic pole (VGP) scatter Sb=21.5 degrees|19.3 degrees 24.0 degrees(N=57) ${{S}_{\mathrm{b}}=21.5{}<^>{\circ}\vert }_{19.3{}<^>{\circ}}<^>{24.0{}<^>{\circ}}\,(N=57)$, the value of which was corrected for within-site dispersion and is little dependent on the choice of the selection criteria. Compared to previous paleodirectional data sets characterizing PSV at various paleolatitudes during the CNS, our Sb estimate confirms a relative latitudinal increase Sb(lambda = 90 degrees)/Sb(lambda = 0 degrees) on the order of 2-2.5. Focusing on PSV at high paleolatitude within the 70 degrees-90 degrees range, we show that Sb was similar to 15% lower at the end of the CNS than during the past 10 Myr, confirming that the singular polarity regime of the geodynamo observed during the CNS is likely accompanied with reduced PSV. Compared to the last 10 million years during which Earth's magnetic field stochastically reversed its polarity similar to 4 times per million year, the Cretaceous Normal Superchron (CNS, 84-121 Ma) represents an anomalously long period of stable polarity, the understanding of which is crucial to constrain the working of the geodynamo. In this effort to better characterize the paleosecular variation (PSV) of the geodynamo, we investigated the paleomagnetic record of lava flow sequences from the Okhotsk-Chukotka Volcanic Belt (NE Russia) emplaced 84-89 Ma at high paleolatitude. First, we obtained that the dispersion of virtual paleomagnetic poles (VGP), used as a proxy for PSV, is 2-2.5 times as high at the paleopole as at the paleoequator. Second, we showed that VGP scatter at high paleolatitude was similar to 15% lower at the end of the CNS than during the last 10 million years, confirming a potential link between polarity regime and PSV. We investigate geomagnetic field behavior at high paleolatitude (similar to 80 degrees N) at the end of the Cretaceous Normal Superchron (CNS)We present a paleodirectional data set from 78 lava flows (resp. 57 directional groups), emplaced 84-89 Ma in north-eastern EurasiaWe show that the dispersion of virtual geomagnetic poles at high latitude is similar to 15% lower during the CNS than for the past 10 Myr